Prior Art Statement
A leach-electrolysis method for producing lead from galena is disclosed by M. M. Wong and H. P. Haver of the U.S. Bureau of Mines in Chapter 37 of World Mining and Metals Technology: Proceedings of the Joint MMIP-AIME Meeting, Denver, Colo., USA, Sept. 1-3, 1976, A. Weiss, Ed. (MMIJ-AIME, 1976). In this process, high grade lead concentrates (about 68 weight percent lead) are leached with ferric chloride and sodium chloride for 15 minutes at 100.degree. C. Lead chloride is crystallized from solution at room temperature and the ferric chloride leachant is regenerated with chlorine. The lead chloride is then reduced by fused salt electrolysis to elemental lead.
B. J. Scheiner and R. E. Lindstrom disclose a chlorine-oxygen leaching technique in "Leaching Complex Sulfide Concentrates Using Aqueous Chloride Oxidation Systems" in the 1978 Mining Yearbook of the Colorado Mining Association, pp 133-38. Lead concentrates bearing about 50% lead are leached in a two-step procedure carried out in a pressure reactor with continuous addition of chlorine and oxygen. The ferric and cupric chlorides extracted from the concentrate by the chlorine and oxygen then react to extract lead and other metals as their chlorides. Lead chloride is dissolved from the leach residue by means of hot brine leach at 90.degree. C., crystallized at room temperature, and the lead is reduced by fused salt electrolysis.
A method for leaching galena with ferric chloride is disclosed by J. E. Murphy, F. P. Haver and M. M. Wong in "Recovery of Lead from Galena by a Leach Electrolysis Procedure", Bureau of Mines Report of Investigations No. RI 7913 (1974). This disclosure concerns itself primarily with the electrolytic reduction of lead from lead chloride, and discloses ferric chloride leaching of the galena ore and dissolution of the formed lead chloride in 25% brine solution at 100.degree. C. Chlorine is used to regenerate the leachant.
A further disclosure by F. P. Haver and M. M. Wong entitled "Ferric Chloride-Brine Leaching of Galena Concentrate" is published in Bureau of Mines Report of Investigations No. RI 8105 (1976). Hot brine (100.degree. C.) and ferric chloride are used to leach the lead chloride from the 68% lead-bearing ore, dissolving the lead chloride as it is formed. Chlorine is used to regenerate the leachant. This is an improvement over the process disclosed in Bureau of Mines Report Number RI 7913, described above, wherein the ferric and brine leaches are not combined.
David M. Muir, Donald C. Gale, A. James Parker, and Dion E. Giles, in "Leaching of the McArthur River Zinc-Lead Sulphide Concentrate in Aqueous Chloride and Chlorine Systems", J. Australasian Institute of Mining and Metallurgy, No. 259 (September, 1976), disclose a number of leaching techniques including leaching with hydrochloric acid, ferric chloride, cupric chloride, oxygen, oxygen and chlorine, chlorine alone, and chlorine with cupric chloride. The cupric chloride leach reported was conducted at 95.degree. C. under carbon dioxide pressure with a 1 M hydrochloric acid concentration. Zinc extraction was about 95% after 2 hours, and the cupric leach was not recommended because of high ferric and cupric concentrations along with the zinc chloride in the leach solution. A further disclosure in this article describes the use of cupric chloride as a catalyst with a hydrochloric acid leach (1 to 5 M HCl). Oxygen pressure is used with this process.
A. B. Bagdasarian discloses "Reduction of Metallic Chlorides by Hydrogen" in 51 Transactions of the American Electrochemical Society, pp 449-494 (1927). The basic reduction reaction is discussed as well as the theoretical aspects of the process. The author discloses hydrogen reduction of lead chloride in closed tubes, with and without bubbling the hydrogen through the lead chloride.